Whether that ire morphed into violence - with Spengler apparently killing his sister before fatally shooting two volunteer firefighters - may never be known. But law enforcement officials think that the pending sale of his house, where Spengler had lived since leaving prison in 1998, unquestionably angered Spengler.

That is one of the theories in a now week-old investigation into the Christmas Eve ambush on Lake Road in Webster. On that morning, Spengler set the house on fire and then lay in wait to shoot responding firefighters.

The real estate agent who worked with Spengler's sister, Cheryl, to buy a house in Henrietta only weeks ago said that she and Cheryl also discussed the sale of the Webster home.

Realtor Laura LaManna of Nothnagle Realtors said the friction between the Spengler siblings was apparent even in the conversations she had with Cheryl.

Cheryl Spengler had mentioned that she lived with her brother in a childhood home, but that the two did not get along, LaManna said. Law enforcement officials say that they suspect that tension could be the root of Spengler's criminal acts.

Unsurprisingly, the police and fire investigation has spread tentacles. The fire remains under investigation. A body found in the charred remains - suspected to be Cheryl - has yet to be identified. And a probe of the guns used by Spengler in his attack on firefighters has led to an arrest of a woman alleged to have bought two of the firearms for him.

Thousands came to Webster on Saturday for calling hours for two West Webster volunteer firefighters gunned down by Spengler - Mike Chiapperini and Tomasz Kaczowka. Chiapperini's funeral was Sunday; Kaczowka's funeral is Monday.

Tracing the guns

The investigation into Spengler's violence started almost immediately after police reached his body Monday on the shore of Lake Ontario.

Spengler, 62, fatally shot himself after engaging in a firefight with police. Firearms were found near him, as was a bounty of ammunition, according to records and law enforcement sources.

Spengler still had several boxes of rounds for his Bushmaster .223-caliber rifle, as well as shells for a Mossberg 12-gauge shotgun, law enforcement officials say.

Those weapons, as well as a Smith & Wesson .38-caliber pistol, were near his body.

The federal Bureau of Alcohol, Tobacco, Firearms and Explosives, or ATF, was running a trace on the weapons within a half-hour, according to an affidavit from ATF Special Agent Sean Martineck.

"Also found in close proximity to (Spengler) was an apparent suicide note, in which Spengler makes reference to obtaining and possessing a Bushmaster and Mossberg," Martineck wrote.

That note alleged that Dawn Nguyen, now 24, bought the firearms for him, authorities say. To do so, she had to sign a federal form affirming the guns were for her.

"Right then and there, it's in pretty bold letters: Are you the purchaser?" William Hochul Jr., U.S. Attorney for the Western District of New York, said Saturday about the form.

Records show that Nguyen did buy the two guns in Henrietta, N.Y., on June 6, 2010.

Law enforcement sources say they're still tracing how Spengler may have obtained the handgun, which is several decades old.

Authorities allege that Spengler was with Nguyen, a Greece resident, when she bought the two guns.

She has been charged with federal and state crimes for allegedly lying on the federal form.

She is free awaiting future hearings on federal charges and is scheduled to appear in Henrietta Town Court on the state charges Jan. 8.

Nguyen has maintained that the guns were stolen from her vehicle. Her mother, Dawn Welsher, alleged in a voicemail left with a Rochester (N.Y.) Democrat and Chronicle reporter that Spengler was "setting us up."

Neighbors

Spengler beat his grandmother to death at 193 Lake Road, the house next door to his home, in 1980. He pleaded guilty to manslaughter, was released in 1998 and successfully completed parole supervision in 2006.

In 1982, Dawn Welsher's parents bought the house at 193 Lake Road.

Law enforcement sources last week linked both mother and daughter to the guns, but only Nguyen was arrested. Nguyen admitted Spengler was with her when she bought the guns.

Welsher's brother, Guy Welsher of Amsterdam, Montgomery County, said he doubted his sister would have supplied Spengler with guns.

"I know my sister. She's not like that. I think the guy might have liked her or something and might have done something like that and blamed her when she turned him off," Guy Welsher said.

The federal and state charges brought against Nguyen - in essence what police call a "straw man" purchase of guns for another individual - are not that common in western New York. Spengler could not legally have guns because he was a convicted felon.

The laws are an impediment to the illegal pipeline of firearms, Hochul said.

Why Nguyen would want the firearms, if not for use by someone else, has not been answered.

"You have to certainly ask yourself why in the world would she need a Bushmaster?" said Assistant U.S. Attorney Bret Puscheck, who is prosecuting the federal case.

There are other federal charges that could be brought if prosecutors decide that Nguyen knew Spengler was a felon and could not legally have guns.

Still, authorities have not indicated that Nguyen had any knowledge that Spengler would one day use the guns for killing.

Monroe County District Attorney Sandra Doorley said her office has yet to decide what if any conditions to request for bail when Nguyen appears in Henrietta Town Court. And she and federal authorities said that the arrest is far from a sign that the police work is over.

"The investigation is still continuing," she said.

That investigation seems to continue to return to the troubled Spengler household.

Somehow, the brother and sister lived under the same roof, but not harmoniously.

LaManna, the real estate agent who worked with Cheryl Spengler, said she only knew Cheryl for three months, and found her charming.

"She was a very nice lady, from what I knew of her," LaManna said.

Of the siblings' relationship, she said, "I knew it was bad, but would have never imagined it would have come to this."